Place the sweet potato on a piece of aluminum foil that is large enough to wrap it for baking. Spray the top and bottom of the sweet potato with cooking oil spray. Sprinkle (or grind) salt on the outside of the sweet potato. Place the sweet potato diagonally in the center of the aluminum foil. Wrap the aluminum foil over the top and up at the ends, so that there will be no leaks from the potato in your oven. (I put the wrapped potato on a baking dish.) Place the wrapped sweet potato in a 350 degree oven, and bake for approximately 1 hour, or until soft when squeezed. (Use a potholder to squeeze.) While your sweet potato is baking, make your Brown Sugar Topping: Mix 3 tablespoons softened butter with 1/4 cup brown sugar until smooth. Place in a small serving bowl. When your sweet potato is done, remove it from the oven, remove the foil, and place your baked sweet potato on a nice serving plate. Cut the sweet potato open, and spoon your desired amount of brown sugar topping into the opening. It will melt and drizzle down the sides. Delish!!!